The overall objective of the proposed studies is to create an interface between three non-human primate research programs to establish ethanol magnetic resonance spectroscopy (MRS) as a translational measure of tolerance. Within the Oregon National Primate Research Center (ONPRC) macaque monkey population, we have previously assessed the genetic basis of innate tolerance to ethanol intoxication, characterized the development of excessive ethanol self-administration, and developed procedures for directly measuring non- human primate brain ethanol via in vivo MRS. We propose to investigate ethanol MRS as a measure of tolerance, by directly determining how it relates to behavioral measures of intoxication, and how it changes with heavy ethanol drinking. In a series of in vivo MRS experiments following intravenous ethanol administration, we have observed that the size of the ethanol MRS signal is a non-linear function of ethanol concentration. We have developed a framework to interpret this finding in terms of the concentration and affinity of a saturable ethanol binding site (or collection of binding sites) within the brain. Our data corroborate early spectroscopic results from human investigations, and provide an opportunity to extend these earlier findings by incorporating modern analysis strategies and a previously unrecognized biophysical model of ethanol binding interactions with macromolecular constituents. Within this context, we will provide the first direct comparison between ethanol MRS measures of tolerance, well-established behavioral measurements of acute tolerance, and the development of acquired tolerance. Each of these measurements will be interpreted in terms of the propensity to self-administer excessive quantities of ethanol, which will also be directly measured in our non-human primate study. First, we will test the hypothesis that a high degree of innate tolerance to the intoxicating effects of ethanol is detectable through an endophenotype of increased BEC- corrected ethanol MRS signal intensity. Second, we will test the hypothesis that BEC-corrected ethanol MRS signal intensity increases as an individual transitions from an ethanol-naive state to a state of excessive ethanol self-administration. Through this work, we aim to develop a translational tool for monitoring neuroadaptations following ethanol exposure that are specifically related to tolerance and propensity for future alcohol abuse. PUBLIC HEALTH RELEVANCE: The goal of this work is to develop a magnetic resonance spectroscopy (MRS) tool to characterize the extent of direct interaction between ethanol molecular constituents of brain tissue. Previous research efforts have revealed promising capabilities of the technique we wish to develop, however they were carried out using human subjects, and thus it was not possible to manipulate the experimental conditions in such a way as to convincingly link the MRS findings to behaviors related to alcoholism. We have made some preliminary findings using non-human primate subjects that we propose to pursue to demonstrate that in vivo MRS can be used to identify individuals that are inherently tolerant to the intoxicating effects of ethanol and at greater risk of developing an alcohol use disorder.